JPS5840582A - Electrically controlled display employing non- linear type element thick in layer and method of manufacturing same - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a screen having a matrix access function that allows an image to be displayed by breaking it down into groups of points or pixels, the pixels being defined by The present invention relates to a screen whose display content changes as a function of control signals applied to a plurality of electrodes. This screen uses materials whose optical properties can be electrically modulated. Control signals are also applied to the electrodes via non-linear resistors that act as switching elements.

The principle of a planar screen is to decompose said screen into MXN identical and approximately square or rectangular pixels that are individually addressable.

The resolution of a screen is a function of the number of pixels each capable of inputting information. Therefore, an electric field must be applied to each pixel. The application of this electric field is easy to imagine if the screen consists of 2.3 dozen point pixels. However, for high resolution screens (more than 1.5 x 10" pixels) it becomes impossible to access each pixel directly using wires. For this reason, the easily realized matrix type We are interested in display devices, where each pixel of the screen is
It is defined as the intersection of two series of orthogonal conductors called "lines" and "columns", and the number of connections is ! 'IX
From N books to M+N books. For high-resolution screens, there are significant gains in terms of wiring.

Addressing one pixel of the screen using control voltages applied to the lines and columns allows the state of the screen to be "refreshed", i.e. restored by cycling, using a time multiplexing method.
lplexing Method),
No need to maintain. This time multiplexing method is physiological and screen ii! ! It is based on the afterglow effect obtained inside the IS. In the case of liquid crystal display means, the cells providing the pixels may be capacitors, the time constant of which is 2.
This is sufficient to hold the charge for two consecutive temporary address operations. A nonlinear resistor is placed in series with a capacitive cell in order to apply a control voltage in a short period of time. Non-linear resistors are varistor-type elements that have an insulating effect on one side of the voltage dark value and a much higher conductivity on the other side. A convenient way to obtain the varistor elements collectively is to use as the substrate a block of varistor material having the same extent and dimensions as the screen. However, this method has many drawbacks.

That is, this method has the disadvantage that stray capacitance cannot be ignored because the nonlinear element has a high dielectric constant. Furthermore, since the non-linear element is generally a varistor of opaque material, the screen itself has the disadvantage of not being usable in transmissive devices.

Therefore, it is an object of the present invention to instead of using a real varistor substrate, which can be transparent (e.g. made of glass) and on which a thick layer of varistor contact members or connections are overlaid, randomly forming a low dielectric constant substrate. It is an object of the present invention to make it possible to eliminate the above-mentioned drawbacks of seeding by using a substrate.

Although the nonlinearity is reduced, the above-described varistor has sufficient characteristics as a screen.

Specifically, the present invention is a display device that displays an image on the surface of a substrate by electrically controlling a plurality of display cells providing pixels, each cell being parallel to the surface of the substrate and staggered with respect to the other. and the first and second electrodes forming the capacitor are made of a material whose optical properties change as a function of the electric field generated, each cell also having a resistance value that changes as the applied voltage decreases. The display device is connected to electrical connections disposed on the substrate by using varistor elements that are functional, and further, the substrate is made of a plate of a heat-resistant dielectric material, and
The varistor element is comprised of a contact member made of a varistor material whose negative surface is on the connection and whose other surface is connected to one of the electrodes closest to the substrate. .

Hereinafter, the present invention will be explained in more detail by way of examples with reference to the accompanying drawings, but the present invention is not limited to these examples.

FIG. 1 shows a partial cross-sectional view of a display device that is a non-limiting embodiment of the invention. The display device comprises a layer l of electroluminescent material, each element of which is controlled by contact members or connections 2 of varistor type resistive material. Using a liquid crystal layer as a material for electrically controlled display devices
Included in the present invention. This liquid crystal layer fills the space interposed between the thin plates or plate members 3 and 4. about 10
Micron spacing is defined using shims not shown.

It is known to apply an electric field to a liquid crystal in order to change the orientation of one molecule of the liquid crystal for the purpose of varying the incident light. Materials with a mesomorphous phase are composed of long molecules that can be oriented in the presence of a solid wall according to a common direction, which may be parallel or perpendicular to the wall surface.

The direction of this alignment depends on the liquid crystal materials and their respective properties. The orientation of the long molecules of the liquid crystal is at a suitable interface to ensure that the pretreatment of the wall in contact with the film (e.g., by cleaning the wall and depositing a film of silicon oxide at an angle) By using an activator,
greatly simplified. As a function of the desired effect, mesomorphous materials are used that have one or the remaining of the three phases: smectic, nematic and cholesteric. The liquid crystal layer 1 includes plate members 4 and 3. It is electrically controlled using electrodes 6 and 7, respectively. Each electrode 6 defines, with its approximately III+2 surface circumference, a cell representing, for example, a pixel of a matrix access screen. The control voltage for the liquid crystal layer l is applied using line and column connections. When these lines and columns connect multiple cells, the control of one cell generates an electrically switched electric field, while the remaining cells that are not switched become a source of undesired electrically interfering electric fields. sell.

For a point on the screen (i, j) defined by line i and column j to which electric field Eij is applied, line i must be at potential Vi and column j must be at potential Vi. As a result of the presence of such a potential in line i and column j, the remaining points of the electroluminescent material can become sources of lower electric fields leading to undesired conditions. In order to eliminate this drawback, it is necessary to ensure that each pixel on the screen starts responding only from a certain threshold value. For this purpose, it is known to use a varistor as a switching element, which is arranged in series with each pixel to be excited.

According to this principle, each pixel on the screen is connected to a varistor (V
OR). This varistor is made of a ceramic material whose conductivity varies well above a threshold value Vs. In this case, the theoretical response depends primarily on the threshold Vs.

That is, when V<Vs, the impedance of the varistor is higher than that of the liquid crystal cell, so no charging current flows. In this case, ■ is the potential at the terminals of the varistor.

Also, when V>Vs, the impedance of the varistor drops and the lighting element receives charging or discharging current.

When the voltage ■ drops below Vs again, the impedance of the varistor becomes higher than that of the liquid crystal again, and the capacitor that the cell forms slowly discharges with a time constant τ proportional to its capacitance and the leakage resistance of the system. . Thus, the above-mentioned h display device is configured to display V<νS during a time shorter than the storage time τ by the newer voltage pulse.
You have to do it. By giving Vs a value significantly higher than the threshold of the electroluminescent material, it is possible to obtain shorter response times and thus higher multiplexing levels N (N - τ). Here, 'r represents the elapsed time between two charge refresh operations, and t is the threshold value Vs
represents the charging time determined by the product RXC in an operating mode exceeding .

Hereinafter, the term "heat resistant" will be used to define a substrate that can withstand increasing temperatures during different manufacturing modes of the screen without any loss of properties.

For example, by using a heat resistant substrate 4 such as Corning J Glass 7059 at an annealing temperature of 635° C., a conductive access line connection 5 having a width of about 100 microns is formed in the recess 16. formed inside. The line connections, parallel to each other and equally spaced, can be photolithographically formed on the vacuum deposited metal layer. In that case a thick layer of varistor contact element 2 is deposited on these lines.

Varistor-based materials are used to make such contact members. This material uses bismuth oxide (Bi203) and manganese oxide (MnO, y
) particles of zinc oxide (ZnO) powder as a coagulant. The material thus prepared is in the form of a dense block providing the starting material for the varistor contact member according to the invention. This material is finely ground into a powder to which a binder, such as glass, is added. The paste obtained from the vanider-doped mixture is applied by screen printing to the line termination surface facing each cell to be excited and then annealed at 520°C. It is also possible to use organic binders in order to be able to screen print the paste onto the above, in which case the firing temperature will be lower than the values mentioned above. The contact member made in this manner has a wall thickness of about 25 microns.

Varistors have a nonlinear resistance value that strongly depends on the applied voltage. Varistors deposited with these thicker layers exhibit much less nonlinearity than varistors made by conventional methods - yet they are still sufficient for displays where the dark value voltage is controlled. It has characteristics. Another thing that can be obtained by following the manufacturing process described above
One advantage is that the varistor type contact member has a low dielectric constant of 148
0 (ε0 is the dielectric constant in vacuum), thereby reducing stray capacitance.

Next, the electrode 6 is deposited using, for example, masking.

These electrodes 6 may be reflective or transmissive depending on whether the screen is reflective or transmissive. When used in a reflective type device, the electrode 6 can be made of aluminum. This aluminum material has excellent specular reflection properties. On the other hand, when used in a pass-through device, a deposited layer of tin oxide or indium oxide or a mixture of these re-oxides may be used in the exemplary manner.

The line connection 5 that applies a control voltage to the electrode 6 has a width smaller than that of the element that has to control the molecular orientation of the liquid crystal. Each of the line connections 5 controls a set of electrodes 6 parallel to it using a varistor type contact member 2. Contact between the electrode 6 and the varistor type contact member 2 is made through a small tongue lO having the same properties as the electrode.

The plate element 3 may be of the same nature as the plate element 4 and carries on its inner surface a transparent column connection 7 which can advantageously be formed from an adhesion layer of soot or an oxide of indium or a mixture of both oxides. . In this embodiment, the above-mentioned column connections 7 are arranged orthogonally to the line electrodes 6, and each column covers all the line electrodes that it traverses.

In liquid crystal screens, the conventional practice is to use crystals with a nematic phase at room temperature, in which one of three effects is used: electrically controlled birefringence, dynamic dispersion modes, and twisted nematic phase. One is used. The last of the three effects described above has the interesting property that linearly polarized light propagating perpendicular to the plate undergoes a rotation of approximately 90". The cell transmits light at rest, but blocks its transmission when an electric field is applied. With such cells, it is often necessary that the plates 3 and 4, as well as the electrodes 6, be transparent. happen.

Since the surface areas of the varistor-type contact member 2 and the line connection 5 are reduced, they do not interfere with light transmission. This fact is an advantage of the present invention. In the prior art, a varistor material was used as a substrate, which material itself is opaque, making it impossible to obtain a screen that would work in a transmissive device.

It is also within the scope of the invention to use mixtures of nematic and cholesteric phases in which mixed particles having a memory effect on the one hand and constituting dichroic pigments and changing the modulation properties of the screen can be mixed on the other hand. In this case, the liquid crystal layer is transparent in the resting state. In order to control the orientation of liquid crystal molecules, it is possible to use the same method as for obtaining the birefringence effect and the dynamic diffusion effect.

A screen that can be used in a reflective device can be easily obtained by attaching an aluminum electrode, which functions as a mirror, to the plate member 4 instead of the transparent electrode 6.

Screens in which each electrode 6 is individually addressed and a plurality of column electrodes 7 are replaced by a single electrode are also encompassed by the invention.

FIG. 2 is a plan view of the screen shown in FIG.
In this figure, it is assumed that the plate member 3 and the liquid crystal layer 1 have been removed. Referring to FIG. 2, the arrangement of the electrodes 6, line connections 5 and varistor-type contact members 2 can be better seen.

FIG. 3 is a partial cross-sectional view of a modified example of a display device equipped with a storage capacitor. In order to extend the data time τ due to the capacitance and leakage resistance of the lighting elements, a storage capacitor can be arranged parallel to each display means. For this purpose, a dielectric layer 8 is arranged on the plate member 4. A third electrode 9 is arranged between these plate members 4 and the dielectric layer 8 in front of each electrode 6 to form a capacitor for each display cell. These dielectrics can be made in the form of thick layers for low resolution screens and thin layers for high resolution screens. The dielectric TM 8 can be made of thick-walled photopolymer, but can also be made by screen printing or thin-walled. In the case of a screen used in a transparent device, the dielectric layer is made thin to make it transparent, and the electrode 9 is made of soot, indium oxide, or a mixture of both oxides. I'm making it.

In addition, when the screen is used in a reflective device, the electrode 9
can be made of aluminum or any other dielectric material. However, in all cases the dielectric layer 8 must not be porous so that the liquid crystal never soaks into it.

FIG. 4 is a plan view of the screen shown in FIG.
The shape and arrangement of electrode 9 are shown. The electrode 6 is common to the display cell and the storage capacitor.

The electrodes 9 are connected to each other along the columns parallel to the column connections 7. This connection is achieved using dielectric strips 11 which are externally connected to columns of the same order or rank.

The present invention also includes arranging the line connection on the outer surface of the plate member 4 instead of the inner surface. (As shown in FIG. 5, which is a partial sectional view of the screen, the so-called "internal structure (Volume 5 structure)"
J is obtained. Recess 12 for line connection 13
is formed on the outer surface of the plate member 4. After this forming step, the electrodes 9, the dielectric strips 11 and the dielectric layer 8, which may be, for example, silica, which is resistant to a firing process, are deposited. Also,
A hole 15 is drilled, for example using a laser, and the varistor 14 is positioned therein; such an assembly is then heated to the firing temperature of the varistor, and then the electrode 6
Attach. Each electrode 6 is thus electrically connected to a corresponding line connection 13 via a varistor element.

This method has the advantage that the line connection does not come into contact with the liquid crystal layer.

The technical idea of the screen according to the invention provides the advantage of eliminating stray capacitances introduced by using a varistor-type substrate.

Such stray capacitance is particularly detrimental when the screen is used in pulses. Another advantage of the invention is the possibility of using the screen in transmissive devices. This method can be used for large screens operating at television speeds.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a display device according to the present invention. Second
The figure is a plan view of the display device shown in FIG. 1. FIG. 3 is a partial cross-sectional view of a display device including a storage capacitor. FIG. 4 is a plan view of the display device shown in FIG. 3. Figure 5 shows the so-called "internal structure (Volume'5)".
FIG. 3 is a partial cross-sectional view of a display device equipped with a structure J. In the accompanying drawings: l: electroluminescent layer, 2: contact member (connection), 3 and 4: plate member, 5: dielectric access line connection, 6 and 7
: first and second electrodes, 8: dielectric layer, 9: third electrode, 1
0: (Small) tongue, 11: Dielectric strip, 12: Recess, 13 Two-line connection, 14: Varistor, 15: Hole, and 16: Recess Applicant Thomson SASF agent Patent attorney Masahiko Arai

Claims (9)

[Claims] (1) A display device that displays an image on a substrate surface by electrically controlling a plurality of display cells providing pixels, each cell being parallel to the substrate surface and staggered with respect to each other, and forming a capacitor. the first and second electrodes are made of a material whose optical properties change as a function of the electric field generated, and each cell also includes a varistor element whose resistance is a decreasing function of the applied voltage. the display device is connected to electrical connections disposed on the substrate; further, the substrate is made of a plate of a heat-resistant dielectric material, and the varistor element has a negative side. A display device comprising a contact member made of a varistor material, which is on the wire connection and whose other surface is connected to one of the electrodes closest to the substrate. (2) the voltage that generates the electric field that controls the cell is
The screen display device according to claim 1, characterized in that the voltage is divided by a matrix system consisting of lines (horizontal rows) and columns (vertical columns). (3) A third electrode is disposed facing the above-mentioned first electrode to form a capacitor on the opposite side of the electrode material, and an insulating layer is formed between the above-mentioned first and third electrodes. The plurality of third electrodes corresponding to the same column are electrically connected to one of the second electrodes via a conductive strip. A screen display device according to claim 2, characterized in that: (4) The screen display device according to claim 1, wherein the electroluminescent material is liquid crystal. (5) The screen display device according to claim 4, wherein the liquid crystal is a mixture of nematic phase and cholesteric phase. (6) The screen display device according to claim 4, wherein the liquid crystal is a twisted nematic phase crystal. (7) The screen display device according to claim 4, wherein the liquid crystal contains a dichroic pigment. (8) A screen according to claim 4, characterized in that at least one surface in contact with the layer is treated to help bring about a preferable orientation of the molecules constituting the liquid crystal. Display device. (9) A method for manufacturing a display screen, the method comprising:
A process of locally arranging a contact member made of a paste based on a varistor material on a heat-resistant plate member with line connections, and a firing process to ensure the heat treatment of said paste. a step of raising the temperature to
A step of arranging a plurality of first electrodes on the above-described fire-resistant plate member so that each of the first electrodes contacts the upper surface of each of the above-mentioned contact members and spreads out, and the above-described first electrodes are combined. positioning the second plate member supporting the second electrode forming the sensor so as to face the heat-resistant plate member, but separating it from the plate member by a space; A method comprising the step of inserting an etchable material into the space between the plate members.